i used gkrellm some years ago and i had problems with compiz and fullscreen flash videos, sometimes with movies
the kde widgets doesn't have those problems atm but since i don't use compiz anymore gkrellm should be ok i think
the problem with it is customize it to look like your desktop, no matter what i do with it, it always looks like it is not part of my desktop, it looks nice but doesn't play nice with the rest of the desktop